In the present state of three-dimensional printing (“3D printing”), much effort has been expended in perfecting the production of plastic and plastic-like articles for appearance models and light-duty functional prototypes. Additionally, a family of high-end laser sintering machines is capable of producing metal parts with impressive accuracy and mechanical properties.
Ceramic materials are somewhat less fully developed. Powdered-substrate 3D Printing is naturally suited for ceramics because conventional ceramic processing has always been based on powders. The use of freeform fabrication over conventional molding and forming processes offers a very attractive expansion of the range of shapes that can be produced, while dramatically reducing the time to produce a part from a CAD model.
The original invention of powdered-substrate inkjet 3D Printing at MIT in the early 1990s used a ceramic powder in combination with a ceramic slurry dispensed through a continuous-jet inkjet printhead. See, e.g., U.S. Pat. Nos. 5,204,055, 5,807,437, and 6,146,567, which are incorporated herein by reference in their entireties. This combination suffered from reliability problems due to instability of the ceramic slurries, and wear on the jetting apparatus.
Later, Z Corporation developed a set of materials using gypsum plaster reinforced with a water-soluble adhesive. See, e.g., various Z Corporation plaster patents such as U.S. Pat. Nos. 6,610,429, 7,087,109, and 7,332,537, which are incorporated herein by reference in their entireties. This approach has the advantage of moving all the chemical reagents into the powder bed, and keeping the jetting fluid water-based and as simple as possible to enhance reliability. It affords high accuracy and reliability, but limits the performance of the product to a temperature range in which gypsum is stable—up to about 1000° C. High accuracy is maintained by the gypsum because it is an ‘active’ filler: It chemically bonds under the action of the solvent (water) in a short period of time relative to the time to dry. This ensures that capillary stresses do not exceed the yield strength of the material, and therefore warping and other problems are avoided.
Extrude-Hone (now EX-One) and VoxelJet used Croning sand, a product bonded with furan resin and catalyzed with methanesulfonic acid (MSA), to build molds for higher-temperature metal castings. MSA was dispensed through a drop-on-demand printhead in an alcohol solution. While this material system opened up new opportunities in high-temperature metal casting, the material is not recyclable and may create a toxic waste problem. See, e.g., EP 1,268,165, which is incorporated herein by reference in its entirety.
To deal with these many problems, a team at MIT developed a powder system based on Portland cement that was recyclable and solidified with a water-based ink. See U.S. Pat. No. 8,211,226, which is incorporated herein by reference in its entirety. This material provides a reliable method to build molds for metals poured up to 1450° C., and some opportunity to go even higher. This material is accurate and reliable, though it depends on the use of foundry sand as a filler, and the fraction of cement in the mix may preclude its use as a general-purpose system for ceramics.